Enabling LZMA for compression to allow us ship more software on our live images.

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Enabling XZ (a variant of LZMA) for compression to allow us ship more software on our live images.

== Owner ==

== Owner ==

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== Current status ==

== Current status ==

* Targeted release: [[Releases/15 | Fedora 15 ]]

* Targeted release: [[Releases/15 | Fedora 15 ]]

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* Last updated: 2010-12-26

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* Last updated: 2011-03-06

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* Percentage of completion: 15%

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* Percentage of completion: 100%

== Detailed Description ==

== Detailed Description ==

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== Scope ==

== Scope ==

* kernel

* kernel

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** Lougher needs to do a new set of patches since the ones for 2.6.34 were only partially accepted.

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** F15 has had 2.6.38 kernels for a while and XZ is working fine.

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*** We are still waiting for Lougher to have a chance to get an acceptable patch (to Linus) for the Linus kernel. If it gets into 2.6.38 we will have no trouble getting this into F15.

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*** Statements from Lougher:

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**** https://bugzilla.redhat.com/show_bug.cgi?id=504425#c19

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**** http://marc.info/?l=linux-kernel&m=127190194229951&w=2

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*** It looks like [http://git.kernel.org/?p=linux/kernel/git/pkl/squashfs-lzma.git;a=summary some patches] were being worked on, but weren't ready for 2.6.35 (or 2.6.36) as there was no pull request for them.

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** [http://sourceforge.net/mailarchive/forum.php?forum_name=squashfs-devel&max_rows=25&style=nested&viewmonth=201011 Discussion] about lzma / xz support in the kernel on the squashfs-devel list.

Owner

Current status

Detailed Description

LZMA compression typically provides better compression than gzip while still providing relatively fast uncompression. Once squashfs file systems are supported by the kernel we can use them for building live images. A test with the games spin resulted in a 8.7% reduction (from 4242538496 bytes to 3873439744 bytes) in size of the resulting live image.

Benefit to Fedora

By allowing more packages to be put on a Live Image, we can make a few of our space constrained images better. For other images, having them be smaller will make them faster to download.

Scope

kernel

F15 has had 2.6.38 kernels for a while and XZ is working fine.

Fallback plan for the kernel is to do nothing.

livecd-creator

Changes to livecd-creator:

Change the default compression type to xz. (Done - in rawhide)

Update the documentation to reflect the changed default. (Done - in rawhide)

These changes won't be made until after the kernel feature is available, so no fallback is needed.

squashfs-tools

The 4.2 release is now in rawhide and F15 testing.

A test case has been created to make it easier to get critical path testing.

Out of scope is taking advantage of squashfs-tools new compression specific options.

They will probably be exposed in some way in livecd-creator for F16 if it looks like they are useful to tweak for live images. But that won't be a feature.

How To Test

We need to make sure live images work.

The nightly builds are now using xz compression.

The Desktop spin from the nightly composes boots successfully from a live USB drive.

We need to make sure live images are smaller using LZMA2 (XZ) compression.

A test games spin from 2011-01-21 rawhide + a 2.6.38 scratch build went from 4499222528 bytes to 4111771648 bytes (8.6% decrease).

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